Heating pad



L R A F c M L R D A P G N I T A E H Filed Dec. 18, 1956 FIG. I.

i Patented Apr. 19;

UNITED STATES PATENr oi-"Flea Ronald Lyman McFarlan, Marblehead Neck,and

v John A. C. Bowleo, Boston, Mass.

Application December 18, 1938, Serial No. 116,514

11 Claims.

hospitals.

Among the several objects of the invention may be noted the provision ofa heating pad of the class described which includes an electric or otherheating element for supplying heat pad, and a heat storing orthermophoric compoenergy to the sition for delivering up said heatenergy as supplied to the pad, over a protracted period of time;

the provision of a heating pad of the class described which is providedwith means automatically regulating the temperature to be achieved bythe pad; the provision of a heating pad of the class described which issubstantially hermeticah 1y sealed, and which is capable of extended useand re-use over long periods of time without a y substantialdeterioration; the provision, in a heating pad of the ciass described,of a new ther mophoric composition of matter, which is adapted todeliver up heat stored therein (such as latent heat of fusion) over agreatly protracted period of time, which composition of matter undergoesa reversible reaction on the introduction and withdrawal of heat theretoand therefrom,

without substantially changing any compositional characteristics overrepeated reversals; and the provision of a heating pad, and athermophorlc composition ofmatter for use therein, which are economicalin construction and operation.

Other objects will be in part obvious and in part pointed outhereinafter.

The invention accordingly comprises the el'emerits and combinations ofelements, features of construction and composition, and arrangements ofparts, which will be exemplified in the structures and productshereinafter described, and the scope of the application of which will beindicated in the following claims.

In the accompanying drawing; in which is illustrated one of variouspossible embodiments of the invention, n

Fig. 1 is a plan view of a heating 'ing the present invention;

pad embodysubstantially substantially Fig. 4 is an enlarged crosssection taken substantially along line 4-4 of Fig. 1; Fig. 5 is a crosssection taken along line 5-5 of Fig. 4.

Similar reference characters in and, substantially dicate correspendingparts throughout the several views of the drawing.

Referring now more particularly to Fig. l, numeral 8 indicates a rubberor like flexible, plastic materiai bag or sack, which is shown as ofgerrerally rectangular shape. The'shape of the tag i. is of noimportance, however. At one end thereof, the bag 9 is formed as a neckor cyiindrical outlet portion t. In the finished pad, the preferred formof the outiet 3 is a solid cylindrical member which embeds a pair ofelectrical com nesting prongs 5 which are adapted to be inserted intothe customary form of electric outlet. However, it is contemplated thatthe prongs 5 may be replaced by other connecting means, such as suitablesocket elements, so that electrical connections may be made to the padby fitting in a plug rather than by plugging the device itself into asocket.

inside the bag i there is provided an electrical heating deviceindicated generally by numeral 1. In the preferred embodiment of theinvention, the device I comprises an electrical resistance heating coil9 embedded in a flexible rubberor like matrix H. The constructionof thisdevice 'I may well be of the type shown in DeLaney et al. Patent2,018,512, dated October 22, 1935. Included in the device i is athermostat I3, likewise embedded in the matrix II. The construction ofthe thermostat 53, which is likewise shown in the aforementioned DeLaneyet al. patent, is indicated for convenience in Figures 4 and 5. Itcomprises a box I! having a cover i1, Mounted in one end of the box ISin such manner as to project into the central hollow portion of the boxl5'i's a bimetallic blade IS. The resistance heating coil 9 is connectedto one end of the blade I! by a connection indicated by numeral 2|. Theother end of the blade I! carries a mov able contact 23, whichcooperates with a fixed contact 25 mounted in the box II, which is inturn connected, exteriorlycf the box 15, with another portion of theresistance heating coil 8.

. The resistance heating coil 9 has .its opposite ends connected to thetwo prongs 5, with the thermostat I; in series therewith. The leads ofthe resistance heating coil 8, indicated by numeral 28 in Fig. 1, areembedded in a neck 21 of rubber or like material which servesstructurally to interconnect the device! and the plug portion 3 of theouter bag i. In the preferred embodiment of the invention, the neck 21connects to the solid portion oi the plug 3 in such manner as to leavean annular trough or or fused together in such manner as to form ahomogeneous, hermetically sealed unit. The final sealing is notordinarily done, however, until after a certain thermophoric compositionto be described, has been placed in the bag.

From Figures 1 and 2, it will be noted that the heating device I hangsrather loosely in the bag I, by means of the neck 21, in such manner asto provide a relatively large free space 3| therein. The free space 3|is filled, in the finished article, with a thermophoric composition. Apreferred thermophoric composition is as follows:

Percent by weight Manganous chloride tetrahydrate (MnClz.4HzO) 3.45Sodium acetate trihydrate (NaC2H3Oz.3I-I2O) 96.55

An alternative thermophoric composition, likewise found to besatisfactory, is as follows:

Percent Manganous chloride tetrahydrate (MnChAHzO) 3.3 Sodium acetatetrihydrate (NaC2H3Oa3I-InO) 9 Glycerine 3.0

Still another satisfactory thermophoric composition is as follows:

1 Percent Manganous chloride tetrahydrate (MnClzAHzO) 3.3 Sodium acetatetrihydrate (NaCzH30z.3HzO) 94.0 Ethylene glycol (CI-IzOHEHzOH) 2.7

If difierent temperatures of operation are desired, the proportions inthe above compositions may be varied without disturbing the desiredaction of the compositions.

In general, the space 3| isbompletely filled with one of thethermophoric compositions above described, or any other suitablethermophoric composition, and the bag then finally hermetically sealed.

The operation of the heating pad as thus described is as follows:

The pad is connected by the prongs 5 to a source of electric current,whereupon the heating device 1 commences to deliver heat, and theelectrically generated heat is stored by the conversion of the sodiumacetate in the thermophoric composition from its crystalline form to itsliquid form. The thermostat l3 shuts ofl the electric current after thecrystalline mixture has been substantially converted into liquid form.Normally, the thermostat II should be set to open the circuit upon theattainment of a temperature not greatly in excess of 75 C. in the pad,because temperatures in excess of this value are sometimes destructiveto the thermophoric compositions above specified.

of changing from the tetrahydrate to the dihydrate form at a temperatureof the order of 58 C., which is approximately the same temperature atwhich sodium acetate loses its water of crystallization. When the meltedmixture is cooling, and giving off heat, the change from manganouschloride dihydrate to manganous chloride tetrahydrate removes water fromthe melt, thus tending to prevent supersaturation of the melt andconsequent failure of the sodium acetate to recrystallize.

The annular trough 29 hereinbefore mentioned likewise aids inpreventingsupersaturation and failure of recrystallization, because it is soformed as to contain a certain amount of the thermophoric compositionwhich, through being removed a greater distance from the heating unit I,usually does not melt during the controlled time interval for themelting of the rest of the thermophoric composition. When coolingcommences, the presence of a small amount of solid thermophoriccomposition in the annular trough 29 serves to seed the crystallizationof the liquid portion of the thermophoric composition, and thus tends toinhibit the formation of supersaturated solutions. Obviously, for thispurpose, the trough 29 may be replaced by any other suitable recess,within the scope of the invention.

In preparing the thermophoric composition, care should be exercised notto expose it to the air for too long a time, such as more than sixhours, because there is a tendency for the man- "ganous chloride to formmanganese hydroxide upon extended exposure to the air.

In operation, the pad should be allowed to come to room temperaturebefore reheating.

Depending upon the size of the pad,.the time required for heating it isfrom the order of ten to the order of fifteen minutes, and the timeduring which the pad will stay hot will vary from the order of ten tothe order of twenty hours. The pad automatically maintains a temperaturein the region of 58 C. for the thermophoric mixtures above given. Thistemperature can be varied somewhat by varying the proportions of theconstituents in the thermophoric composition. The figure of ten totwenty hours (during which the pad will stay hot) has beenexperimentally ascertained and found to hold true for an eight hundredgram quantity of the thermophoric composition.

While in the foregoingdescription details have been given for themechanical structure of a preferred embodiment of the invention, it willreadily be seen that the mechanical form of the invention may be widelyvaried without departing from the spirit of the invention.

Nor is the above description to be considered as limiting the inventionto the particular thermophoric composition described, as manyothersuitable compositions may be satisfactorily used in the generalcombination, either to achieve different temperatures, during theprolonged cooling period, or for other reasons. However, it is to benoted that the thermophoric compositions herein described, which arebelieved to be novel with the present invention, are particularlyadvantageous for use in connection with the heating pad of the presentinvention/because of their characteristics hereinbefore given, andbecause they are capable of sustaining a temperature that so nearlyapproximates the desired temperature for a heating pad of the generalcharacter here concerned.

An incidental advantage of the heating shown in the present invention isthat it can be heated by means other than the electric current. Forexample, the pad shown in Fig. 1, in the event of non-availability ofelectric current, may be heated simply by dropping'it into a pan ofboiling water for a suflicient length of time to bring substantially allof the thermophoric mixture to a liquid condition (this can readily beascertained by feeling the bag and noting its relative rigidity as theheating progresses). Thereafter, the bag can be removed from the hotwater and it will 'give off heat over a protracted period of time inmuch the same manner as if it had been heated electrically,

By making pads of associated elements of rubber, a flexibility isprovided which is distinctly advantageous in pads of this type, since itpermits the pad to conform to the part of the body with which it isplaced in contact. However, such flexibility is sometimes not necessary,and in that event, it is within the scope of the present invention tomake the pad out of metal, fiber, or any other suitable containermaterial.

The thermophoric compositions herein set forth are separately claimed inour copending application Serial No. 173,220, filed November 6, 1937.

In view of the above, it will be seen that the I several objects of theinvention are achieved and other advantageous results attained.

As many changes could be made in carrying out the above constructionsand compositions without departing from the scope of the inven tion, itis intended that all matter contained in the above description or shownin the accompanying drawing shall be interpreted as illustrative and notin a limiting sense.

We claim: 1. In a heating pad, 9. container, a thermophoric compositionwithin said container, and electrical resistance means within thecontainer for supplying heat to said thermophoric composition, saidcontainer comprising a bag made of a flexible material.

2. In a heating pad, a container, a thermophoric composition within saidcontainer, and means within the container for supplying heat to saidthermophoric composition, said container comprising a bag made of aflexible material, said heating means comprising an electricalresistance heating unit embedded in a flexible a thermostat in thecontainer in series with said electrical resistance heating element,said thermostat being adapted to disconnect the element from a source ofelectricity when the temperature of the pad reaches a predeterminedvalue.

5. In a heating pad, a container, a thermophoric composition within saidcontainer, and means within the container for supplying heat to saidthermophoric composition, said container having an interior recess at apoint relatively remote from the heating means, the said recess beingadapted to contain a portion of said thermophoric composition andsubstantially maintain it against melting while the remainder of thethermophoric composition is melting under the heating influence of saidheating means.

6. In a heating pad, a container, a thermophoric composition within saidcontainer, means within the container for supplying heat to saidthermophoric composition, said means comprising an electrical resistanceheating element, and a thermostat in the container in series with saidelectrical resistance heating element, said thermostat being adapted todisconnect the element from a source of electricity when the temperatureof the pad reaches a predetermined value, said container having aninterior recess at a point relatively remote from the heating means, thesaid recess being adapted to contain a portion of said thermophoriccomposition and substantially maintain it against melting while theremainder of the thermophoric composition is melting under the heatinginfluence of said heating means.

7. A heating pad as set forth in claim 5, in which the containercomprises a rubber sack.

8. A heating pad as set forth in claim 6, in which the containercomprises a rubber sack.

9. In a heating pad, a container, a thermophoric composition within saidcontainer, and means within the container for supplying heat to saidthermophoric composition, said thermophoric composition comprising amixture of sodium acetate trihydrate and manganous chloridetetrahydrate.

10. In a heating pad, a container, a thermophoric composition withinsaid container, and means within the container for supplying heat tosaid thermophoric composition, said thermophoric composition comprisinga mixture of sodium acetate trihydrate and manganous chloridetetrahydrate, the sodium acetate trihydrate constituting more than theorder of 90% of the mixture.

11. In a heating pad, a container, 2, thermophoric composition withinsaid container, and means within the container for supplying heat tosaid thermophoric composition, said thermophoric composition comprisinga mixture of sodium acetate trihydrate and manganous chlo-- ridetetrahydrate, together with a small proportion of a liquid selected fromthe class composed of glycerine and ethylene glycol.

RONALD LYMAN MCFARLAN. JOHN A. C. BOWLES.

